Chair backrest



FIG. 1 is a perspective view of a chair backrest showing our new design;

FIG. 2 is a front orthographic view thereof;

FIG. 3 is a rear orthographic view thereof;

FIG. 4 is a right side orthographic view thereof;

FIG. 5 is a left side orthographic view thereof;

FIG. 6 is a top orthographic view thereof; and,

FIG. 7 is a bottom orthographic view thereof. 

The ornamental design for a chair backrest, as shown and described. 